Conventionally, an electrically conductive paste prepared by mixing or compounding a solvent, a resin, a dispersing agent and so forth with an electrically conductive metal powder, such as silver or copper powder, is used for forming electrodes and electric wirings of electronic parts by a printing method or the like.
However, silver powder increases the costs of the paste since it is a noble metal although it is a good electrically conductive material having a very low volume resistivity. On the other hand, the storage stability (reliability) of copper powder is inferior to that of silver powder since copper powder is easily oxidized although it is a good electrically conductive material having a low volume resistivity.
In order to solve these problems, as metal powders for use in electrically conductive pastes, there are proposed a silver-coated copper powder wherein the surface of copper powder is coated with silver (see, e.g., Japanese Patent Laid-Open Nos. 2010-174311 and 2010-077495) and a silver-coated copper alloy powder wherein the surface of a copper alloy is coated with silver (see, e.g., Japanese Patent Laid-Open Nos. 08-311304 and 10-152630).
However, in the silver-coated copper powder disclosed in Japanese Patent Laid-Open Nos. 2010-174311 and 2010-077495, if a part of the surface of copper powder is not coated with silver, the oxidation of copper powder progresses from the part, so that the storage stability (reliability) of the silver-coated copper powder is insufficient. In the silver-coated copper alloy powder disclosed in Japanese Patent Laid-Open No. 08-311304 or 10-152630, there is a problem in that it has a high volume resistivity (a low electrically conductivity), so that the storage stability (reliability) thereof is very low.